The overall goal of this project is to understand how pistil S-Rnase of Petunia inflata discriminate between self pollen and non-self pollen during self-incompatibility interactions. Since the use of RNases as recognition molecules is unique to this type of self-incompatibility, this study will uncover a new model for cellular recognition in biological systems. Furthermore, a number of medically important proteins have been shown to be RNases, e.g., angiogenin which is involved in the vascularization of tumor cells, and two major proteins in the secretory granules of cytotoxic eosinophils which play a role in the immune defense system. Hence, the study of S-Rnase will also expand the scope of the understanding of the biological functions of RNases. The specific aims are 1) to use transposon insertion mutagenesis to identify the so far elusive pollen component of self-incompatibility in order to understand how S- RNases discriminate between self and non-self pollen; 2) to introduce S- Rnase/GFP (green fluorescence protein) fusion constructs into transgenic plants to study whether rejection of self pollen results from allele- specific uptake of S-RNases into pollen tubes.